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I recently bought a 2005 BMW X3 2.0d. There is a rattling / click sound from the rear left wheel when pulling off in 1st gear and with change over into 2nd. the same sound is heard when turning right on pull off.

Supa Quick CV fitment assured me that it is not the CV Joint. They rather replaced the rear shocks which was needed.

A machanic at the local service centre greased the CV boots and could not find the origin of this sound. Suggestions or help would be highly appreciated.

Checked heat shields and pipe hangers which are all still fine. No problem with butterfly flap when idling or reving motor. Tried driving with DSC off noise level slightly lower can hardly hear ratling (cluck-cluck) sound. Also tried braking hard with no success.

Putting the left wheel on a jack, leaving it in 1st gear, the wheel can be rocked slightly backward and forward by hand.

1) Are you sure is not the differential? X3's have a tendency to "whine" in the rear differential which is actually normal. There's a solution, however, that BMW has which is to replace your fluid with new BMW Rear Diff + FM which stands for "friction modifier." I have that sound and it worries me but I'd rather not change the fluid and it's not constant anyways. Happens sporadically.

2) You said you lifted the wheel and you can rock the wheel backward and forward? I want to make sure you don't mean to say you can "rotate" the wheel backward and forward which is logically normal. However, if you can literally ROCK the wheel backward and forward by hand, (in other cars and make) that's usually the wheel bearing which you would have to replace. However, a bad wheel bearing usually doesn't "rattle", instead if humsss...

Does the rattle occur when driving straight or when turning? My differential clunks when I do sharp turns on 1st or 2nd gear. In my case, it only happens at slow speeds.

At first I thought it could be the tyres, but the problem still happens after replacing all four identical tyres. Mine is a 3.0 TD. I will be replacing the differential oil in the next few week and will let you know if that fixed my problem.

It is but please do not. Get an ECU re-map instead. Much better. I could get long winded on this but having been there and done that (tuning box for 20k then ECU remap for 40k) the ECU re-map is better, much better IMO.

oh one extra point. The tuning box will give apparent gains in economy but in fact it is cheating. The ECU thinks it is delivering x amount of fuel, the tuning box adds more that the ECU is unaware of. The ECU only records what it "thinks" it has used. End result is understating of fuel consumption when the tuning box is used. e.g. I would get 6.5ltr per 100km on the highway with the tuning box where in fact with the stock X3 I get 7.0ltr per 100km and with the ECU remap 7.5 per the ECU or rather the on board computer. The 7.0 and 7.5 are accurate, the 6.5 was incorrect as a simple distance measurement on full tank will tell you. So I lose economy (a tad) but the power and torque gains more than make up for this in grin factor.

The cause to this problem is the damper mechanism in the muffler. European Countries has strict sound regulations which requires that the vehicle engine running is also quiet. In the muffler there is a damper plate that is vacuum line powered. When the engine is running at low RPM conditions, the damper is closed which is controlled by the vacuum from the engine. As the engine power is increased, the damper opens under vacuum. As the vehicle ages, the vacuum line can leak due to drying out of the line material. The rattle that you are hearing may be due to the vacuum line leaking such that the damper cannot come fully open when it needs to so that it rattles on the stops.

With your vehicle off, you can look into the exhaust pipes and see that one of them has a metal plate blocking it closed. Start the vehicle and have another person pulse the throttle while you stand behind the vehicle and look into the pipe while the engine is running, you will see the damper plate open and close.

If over 60k miles, you'll want to change the differential fluids anyway. Despite claims to the contrary, no fluid is "lifetime." "Lifetime" simply means it will last the life of the warranty. Diff fluid replacement is cheap and easy, and goes along way towards preservation of the vehicle's drivetrain.